Precise and reliable onsite detection of methyl mercaptan (CH 3 SH) is of great significance for environmental surveillance. Here, we synthesized a novel blue fluorescence nanozyme CeO 2 @TPE with high peroxidase-like activity by employing aggregation-induced emission (AIE) tetraphenylethene (TPE) to embed into hollow CeO 2 nanospheres. In the presence of ethanol oxidase (AOX) and o-phenylenediamine (OPD), we engineered an enzymatic cascade activation ratiometric fluorescence−colorimetric dual-mode system AOX/CeO 2 @TPE + OPD toward CH 3 SH. In this design, CH 3 SH initiated AOX catalytic activity to convert it into H 2 O 2 for activating the peroxidase-like activity of CeO 2 @TPE, producing • OH for oxidizing the naked-eye colorless OPD into deep yellow 2,3-diaminophenazine (DAP) with an absorption enhancement at ∼425 nm, companied by a new emission peak at ∼550 nm to match with the intrinsic emission at ∼441 nm for observing ratiometric fluorescence response, enabling a ratiometric fluorescence−colorimetric dual-mode analysis. Interestingly, both the ratiometric fluorescence and colorimetric signals could be gathered for being converted into the hue parameter on a smartphone-based sensor, achieving the onsite visual fluorescence−colorimetric dual-mode detection of CH 3 SH in real environmental media with acceptable results. This study gave a novel insight into designing target-responsive enzymatic cascade activation system-based efficient and reliable dualmode point-of-care sensors for safeguarding environmental health.

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The development of facile, reliable, and accurate assays for pathogenic bacteria is critical to environmental pollution surveillance, traceability analysis, prevention, and control. Here, we proposed a rolling circle amplification (RCA) strategy-driven visual photothermal smartphone-based biosensor for achieving highly sensitive monitoring of Escherichia coli (E. coli) in environmental media. In this design, E. coli could specifically bind with its recognition aptamer for initiating the RCA process on a magnetic bead (MB). Owing to the cleaving of UV irradiation toward photoresponsive DNA on MB, the RCA products were released to further hybridize with near-infrared excited Cu x S-modified DNA probes. As a result, the photothermal signal was enhanced by RCA, while the background was decreased by UV irradiation and magnetic separation. The correspondingly generated photothermal signals were unambiguously recorded on a smartphone, allowing for an E. coli assay with a low detection limit of 1.8 CFU/mL among the broad linear range from 5.0 to 5.0 × 105 CFU/mL. Significantly, this proposed biosensor has been successfully applied to monitor the fouling levels of E. coli in spring water samples with acceptable results. This study holds great prospects by integrating a RCA-driven photothermal amplification strategy into a smartphone to develop accurate, reliable, and efficient analytical platforms against pathogenic bacteria pollutions for safeguarding environmental health.

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